Effect of fluoride incorporation into human dental enamel on its demineralization in vitro

Coronal surfaces of extracted human teeth were ground to a depth of about 1 mm and then cut in half labiolingually. One half was used as a control; the other half was exposed, for 3 days, to a fluoride-enriching buffer (0.1 mol/l lactic acid, 19.7 mmol/l CaCl2, 10.8 mmol/l KH2PO4, 3 mmol/l NaN3; pH adjusted to 4.68 with KOH) having fluoride concentrations from 0.0002 to 2.2 parts/10(6). This exposure resulted in an uptake of fluoride by the enamel to a depth of 2 microns without any apparent demineralization. The fluoride uptake was proportional to the F concentration of the enriching solution, reaching concentrations of about 8000 parts/10(6) within the first micrometre of enamel exposed to the highest F concentration; the controls had uniform F concentrations not exceeding 50 parts/10(6) along the 2.5 microns of enamel depth sampled. Thin sections (140-160 microns) were cut perpendicularly to the lingual surface, coated with protective resin except for a window about 1 mm long on the ground lingual surface, and exposed to a demineralizing buffer. The mineral losses of the sections were followed over 5 days by microradiography and image analysis. Fluoride enrichment resulted in reduced demineralization and the reduction was inversely related to the enamel fluoride content. The controls displayed a uniform erosion of the surface enamel whereas all the treatments below 1.5 parts/10(6) in the enriching solutions developed typical subsurface 'lesions'. The mineral content of the surface layer increased with increasing time of exposure to the demineralizing buffer.(ABSTRACT TRUNCATED AT 250 WORDS)